Swift自定义操作符

在Swift中，自定义操作符就是简单的二步：首先在全局使用operator关键字来声明操作符，同时用prefix、infix或postfix来声明操作符的位置；然后在所需要的类/结构体中实现操作符。如下代码所示：

postfix operator >?
postfix operator >!

extension MIType {
    public static postfix func >?(type: MIType) -> MIType {
        return MIType("Optional<\(type.name)>")
    }
    
    public static postfix func >!(type: MIType) -> MIType {
        return MIType("ImplicitlyUnwrappedOptional<\(type.name)>")
    }
}

自定义操作符需要以两类字符开头：

1. ASCII字符中的/, =, -, +, !, *, %, <, >, &, |, ^, ?, ~
2. Unicode中的Mathematical Operators, Miscellaneous Symbols和Dingbats Unicode blocks这些字符中的字符

然后后面允许使用组合的Unicode字符。如下代码是以一个Miscellaneous Symbols开头的实现向量加法的操作符。

infix operator ★+

struct Vector2D {
    var x: CGFloat
    var y: CGFloat
}

extension Vector2D {
    static func ★+ (left: Vector2D, right: Vector2D) -> Vector2D {
        return Vector2D(x: left.x + right.x, y: left.y + right.y)
    }
}

let vector1 = Vector2D(x: 10, y: 20)
let vector2 = Vector2D(x: 30, y: 10)

let vector = vector1 ★+ vector2

vector.x		// 40.0
vector.y		// 30.0

参考

1. The Swift Programming Language (Swift 4) – Advanced Operators
2. [The Swift Programming Language (Swift 4) – Lexical Structure](